The Cathédrale Notre-Dame de Chartres is massively impressive in many ways— its pure Gothic design and decoration, its brilliant stained glass windows—but it is just as impressive in the parts you cannot easily see, or see at all, from ground level.

For a small fee, you can take a guided tour that climbs 200 spiral steps to the towers of the church, wanders along the parapets, and ducks into the huge space over the nave and below the roof.

The panoramic views of the town and surrounding countryside are marvelous up there, of course, and so is what you learn about how this mammoth masterwork was built, and how it has been preserved.

The cross in the cast ironwork supporting the roof...

During the visit you will stop a couple of times on balconies where you can see the back of some of the stained glass windows and get an appreciation for how these marvels were made and maintained.

The intricate pictures are made of colored glass fragments held together by lead strips called cames. A medieval system of iron and steel straps, bars, and pegs keep the windows together. Since these items rust over time, they must be restored periodically. As you wander along the roof, you can see that some of the windows are now protected by translucent exterior coverings, while others are still open to the elements and awaiting protection.

The guide points out the construction and restoration of some of the stained glass windows of Chartres Cathedral. This is about half way up to the roof line.

After appreciating the beauty of the stained glass, it is a fascinating complement to see what lies behind the beauty, and what it takes to maintain it. Walking along the roof line is an extraordinary experience—gorgeous views of the town, a new perspective on the stained glass, a bird's eye view of the buttresses, and a growing appreciation for the design and construction of the entire cathedral and its roof.

Note that as of this writing visitors cannot access the top of the towers. The visit goes along the roof line and under the roof, but not up the towers. The towers may re-open in the future.